1. Technical Field
This invention relates to the technology of inoculating aluminum castings with grain refining agents and particularly to the manner of inoculation that eliminates contaminants, reduces the required amount of inoculant, and achieves an improved distribution of inoculant without need for augmented circulation.
2. Discussion of the Prior Art
As aluminum engine blocks are designed for higher stressed applications, microstructures of conventional aluminum alloys may not withstand the imposed loads over increasingly longer useful lives for the blocks, particularly at high stress locations such as integral crankshaft bearing yokes.
The prior art as heretofore attempted to improve the yield strength of aluminum alloys by bath inoculation of molten aluminum with small amounts of titanium and boron to achieve a finer grain size of the cast microstructure. Unfortunately, such open bath inoculation, prior to pouring of the molten metal, allows ingress of contaminants, allows the inoculant to settle in the bath as sludge, and requires an excessive amount of inoculant to ensure dissolvement throughout all of the charge of aluminum and to overcome the fading of the inoculant with time. Moreover, bath inoculation is demonstratably a high cost method.
Applicant is unaware of any attempts to inoculate a molten aluminum casting charge in its path from the pouring basin or holding crucible to the mold, except by use of a wire feed inoculant pointed into the aluminum stream to be progressively melted. Wire inoculation is expensive and permits contamination by films adhering to the surface of the wire.
Titanium and boron have been introduced to a stream of pure aluminum metal for creating grain refining bars which bars are later used to inoculate a molten bath. Unfortunately, such teaching has little to do within the mold inoculation of the final casting charge. In these inoculant- bar-forming techniques, powder titanium and/or boron is dumped into the stream of aluminum usually in an open trough, which technique fails to overcome many of the problems of bath inoculation.